CARDIAC: CARDboard Illustrative Aid to Computation

[Thomas Klemm]

(10-11-2014 10:16 PM)Don Shepherd Wrote:  I got one of those from Bell Labs in the 1970's. I already knew programming (FORTRAN) at the time. I played with it for awhile, but it really didn't teach me anything important that I didn't already know from programming school (including IBM assembly).

I like how simple it is. The boot-loader program is just two instructions:

002 INP 02
800 JMP 00

And still it's powerful enough to provide:

• Indirect Loads
• Indirect Stores
• Array Indexing
• Stacks
• Subroutines
• Recursion
  

Who would think, that you can run "Towers of Hanoi" on it? But I admit it's more like a punishment if you ask someone to run it for 5 disks on the real hardware. However it's fun to watch it running in the simulator in slow motion.

It was new to me how subroutines are provided:

Quote:In the CARDIAC, the JMP instruction is effectively a jump-to-subroutine instruction, storing the return address in location 99. Because the address stored in location 99 is prefixed by the opcode 8, the instruction in that location becomes a return-from-subroutine instruction. Thus any segment of code whose last instruction is at location 99 can be called as a subroutine, simply by jumping to its first instruction. For example, a simple routine to double the value of the accumulator could be coded as:

Code:

97      696     double  STO     96
98      296             ADD     96
99      800             JMP     00

and the subroutine can be called with a jump to double:

Code:

        897             JMP        double

Thus I definitely learned something.

(10-11-2014 10:16 PM)Don Shepherd Wrote:  I think it is designed for those who don't know anything about programming but want to learn a bit.

As far as I know it's from a time where access to a computer was difficult.

(10-11-2014 10:16 PM)Don Shepherd Wrote:  I've still got it, by the way.

In the manual a program to play "Single-Pile Nim" is developed. A slightly different rule is used as you may not remove the same amount of pebbles as your opponent during his turn. In other words, if your opponent has just taken two pebbles, you may take one or three, but not two.

You could take it to school and let the your pupils play. There's also a kit they could assemble themselves.

Cheers
Thomas